Immunoassays have found widespread application in the field of clinical diagnostics for the detection and measurement of antigens, antibodies, drugs, vitamins, hormones, metabolites and other substances of interest in biological and non-biological fluids. Typically, these analytes occur in micromolar (20.sup.-6 M) or less concentration.
With the discovery of the human immunodeficiency virus (HIV) and its role as the cause of AIDS well established, much effort has focused on the development of immunoassays for antibodies to HIV viral components in biological fluids. Other assays have been designed to detect HIV viral antigens. The most commonly employed antibody screening assay is an enzyme-linked immunoadsorbent assay (ELISA) using whole virus lysates adsorbed to a solid phase, such as a microtiter well or bead. These assays typically involve long incubation periods and thus require as much as 3-4 hours to perform. More rapid tests have been developed based on agglutination of microparticles coated with viral proteins, but these assays are sometimes difficult to interpret and present problems of sensitivity and specificity.
Immunoassays such as ELISAs are referred to as heterogeneous because the signal emitted by a bound labelled reactant is indistinguishable from the signal emitted by free labelled reactant and thus a separation step is required to distinguish between the two. These assays typically employ at least one reactant immobilized on a solid phase to effect such separation. Solids used to immobilize reactants in immunoassays have included controlled pore glass and preformed polymers, such as polyvinyls, polyacrylamides, polydextrans, and polystyrenes. Numerous separation methods are known in the art and have been used in heterogeneous immunoassays. These include centrifugation, microfiltration, affinity chromatography, and gel-permeation chromatography. Since the kinetics of reaction between an immobilized antibody (or antigen) and its binding site tend to be slower than the kinetics of the same reaction occurring in solution, long incubation times are frequently required. When the multiple wash steps often needed are considered, it can be appreciated that heterogeneous assays tend to be time-consuming and labor-intensive.
There is a need in the art, then, for an HIV immunoassay which is highly sensitive, has fast-reaction kinetics, and which is readily amenable for use in efficiently detecting the presence of a variety of HIV analytes within a home or clinical setting. The present invention fulfills this need and further provides other related advantages.